Hydraulic fracturing is a process in which an underground geologic formation that is disposed adjacent to a bore hole is fractured by injecting a pressurized material in order to extract a desired substance, such as oil and/or a gas (such as natural gas), from the geologic formation. The injection of the pressurized material creates channels, i.e., fractures, in the geologic formation through which the desired substance may flow to the bore hole and be retrieved. In this process, the material injected into the geologic formation is often a liquid carrying solid particles that are often referred to as a proppant. Proppants are often particles, such as sand, that have a coating disposed on the particle. The proppant migrates into the fractures that are formed and holds them open so that the desired material can flow out of the fracture.
One problem for many existing proppants, particularly those used in low temperature (no more than 150° F.) wells, is that of inadequate crush resistance. Crush resistance refers to the ability of a proppant to resist breaking down at high pressure. A proppant with poor crush resistance would fail to effectively prop open fractures in the geologic formation and can contribute to the inclusion of dust particles in extracted fuel substance. Yet another problem, even with proppants that initially exhibit good crush resistance, is their inability to maintain such good crush resistance over time. In other words, they exhibit poor shelf-life stability.
In addition, materials derived from renewable resources are becoming more commercially desirable due partly to the increasing cost of petroleum-derived feedstocks. The “green” image of renewable-based products has also become a significant factor in the marketing of various products; however, the physical characteristics and properties of, for example, any coated proppants produced using such materials should not be detrimentally effected as compared to those produced from petroleum-based materials. In addition, retailers and government agencies are pushing for higher renewable resource content in the finished goods they sell or purchase to take advantage of this “green” image or to reduce the dependence on petroleum-based materials.
As a result, it would be desirable to provide improved coated particles that can be used, for example, as a proppant in hydraulic fracturing in which the proppant has good crush resistance as measured by unconfined compressive strength (“UCS”) and also has the ability to retain its UCS over a significant period of time, i.e., it has extended shelf life stability. Moreover, it would be further desirable to provide such particles in which the coating is derived from a significant amount of biobased/renewable material.
The inventions described in this specification were made in view of the foregoing.